This invention relates to a method of determining a speech parameter, for example the pitch, as a function of time in a speech signal, and to a system for carrying out the method.
Hereinafter the invention will be explained in more detail with reference to a method and a system for determining the variation of the pitch as a function of time. It should, however, be stated that the invention is of wider applicability and could also be used to determine, for example, one or more formants of the speech signal as a function of time.
For a number of applications, such as analysis and resynthesis of speech and investigation of intonation contours, the variation of the pitch as a function of time in continuous speech has to be measured. This appears to be a fairly complex problem and there are not any pitch meters which do not make any measuring errors. On the other hand, the speech quality after analysis/resynthesis is to a considerable extent, determined by the correctness of the measured pitch contour. It is therefore of important to have pitch meters which make few measuring errors. For this purpose a method which calculated the pitch in the frequency domain was developed in the past by Duifhuis, Willems and Sluyter. This method, which is known under the name of & harmonic sieve, is known, inter alia, from the published Dutch Patent Application No. 7812151 which corresponds to U.S. Pat. No. 4, 384,335 (5/17/83). In this method (i) in a first step time segments of the speech signal are derived from the speech signal at m time instants which regularly follow each other, and from each time segment i(1.ltoreq.1.ltoreq.m) there is degree a measure of fit p(i,j) which is associated with the time segment and which, for a series of n possible values for the speech parameter, in this case the pitch, indicates how well a chosen value f.sub.j for the speech parameter (1.ltoreq.j.ltoreq.n) fits the speech signal of the relevant time segment. The variation of the speech parameter in the speech signal as a function of time can then be determined in various ways from the degree of fit.
In view of the results obtained by means of the known method, the method for determining the pitch never-the-less appears still to be in need of improvement.